Originally Posted by 62vette
Wattsy, what hub is it?
Freehubs for Shimano 8 & 9 speed will do 10 speed with a spacer added (comes with a 10sp cassette.) 10 speed specific hubs (like the Dura Ace wheels) will only do 10sp as they are too narrow for 9sp.
Mavic hubs need a spacer for 8sp & 9sp (comes with the hub) and for 10sp you need the Mavic spacer plus the Shimano spacer.
Correct me anyone if I am wrong.
I've just put the 9 speed cluster on the 10 speed hub. I used a spacer from an old 9 speed cluster and it fits perfectly. Went for a test ride up and down the street and it shifts perfectly as well. BTW, it's a Shimano hub/cluster.
The wheel had a 10 speed Dura Ace cluster and used a medium and small spacer to keep it tight.